1. Field of the Invention
This invention relates to novel human interleukin-2 polypeptide derivatives, to recombinant plasmids with DNA fragments coding for said polypeptide derivatives being inserted therein, to microorganisms harboring said plasmids and to a method of producing human interleukin-2 polypeptide derivatives using said microorganisms.
2. Description of the Prior Art
Interleukin-2 (hereinafter abbreviated as IL-2) is a lymphokine produced by T lymphocytes. Binding of the receptors on the surface of activated T-cells, IL-2 is not only essential for proliferation of antigen-stimulated T cells but also bestowed with physiological activities, such as the ability to enhance the generation of cytotoxic T lymphocytes and the ability to activate natural killer (NK) cells. Accordingly, IL-2 is expected to be useful in clinical applications for the treatment of immunodeficiency syndrome or for antitumor immunotherapy. The human IL-2 polypeptide derivatives according to the invention also have IL-2 activity and are expected to be useful as drugs in the same way as IL-2.
The rapid progress in recombinant DNA technology in recent years has made it possible to produce in large quantities in microorganisms those substances that are produced only in small quantities in eukaryotic cells and accordingly are difficult to isolate.
The nucleotide sequence of the cDNA coding for IL-2 has been determined by Taniguchi et al. through cloning, in Escherichia coli, of a cDNA derived from the human T-cellular leukemia cell line Jurkat-111 and by Shimada et al. through cloning of a human tonsillar cellderived cDNA in Escherichia coli [Taniguchi et al.: Nature, 302, 305 (1983); Shimada et al.: Biochem. Biophys. Res. Commun., 115, 1040 (1983)]. When the IL-2 DNA cloned by Shimada et al is inserted into the tryptophan promotercontaining vector pKYP10 (U.S. patent application Ser. No. 06/452,290 corresponding to Published Unexamined Japanese Patent Application No. 110600/83) and expressed in Escherichia coli, the IL-2 can be produced in large quantities.
The IL-2-encoding cDNA cloned by Shimada et al. has the nucleotide sequence shown in FIG. 1.
As for IL-2 derivatives, it is reported that substitution of serine (Ser) for the 58th amino acid cysteine (Cys) or Ser for the 105th amino acid cysteine leads to a reduction in specific activity to 1/50 to 1/100 of that of the parent IL-2. Substitution of Ser for the 125th amino acid Cys is said to increase in specific activity by 30% [A. Wang et al.: Science, 224, 1431 (1984)].